Effect of long sweep 90s on a washing machine drain line

A (plumbing-knowledgeable) family friend (whose father is a master plumber) agreed to install the drain/vent lines for a stackable washing machine/dryer combo into a top-floor condo my girlfriend just bought (which I'm doing a total rehab on.) His plan was to tie the 2" waste into the 3" section of pipe between the toilet closet bend and the fitting at the vertical vent/waste line (see attachments, for existing DWV.) The friend can no longer assist so, I decided to tackle the task myself... While I'm a competent DIYer, DWV plumbing is my weakest skill so I spent a lot of time researching how to approach the job. Unfortunately -or, more correctly, fortunately- I learned earlier today (through this forum) that -despite him having "checked with Dad"- his design isn't feasible as it isn't code-compliant, and would cause the toilet to gurgle (at a minimum) and would/could also cause the water in its trap to be syphoned out.

So, I have only one alternate route for the waste line, and it involves making two, 90 degree turns within the first four feet of the washer's trap. I'd use long sweep 90s (none of the walls are load bearing so, I can use some "create framing" to make this happen within the 2x4s) but, I need to know if this approach will work (that is, the proximity of the elbows won't constrict the discharge.) If it will work, I'd also appreciate advice as to the type of fitting I should use to connect to the 3" vent/waste line. Finally, I know that I also need a separate vent... it will start after the trap, and will connect above the existing, highest branch (?) vent that comes up from the two condos below. Does this need to be 2" or, will 1.5" be okay?

Thanks, Gary

Images (in order):
locn I was told we would tie-into
x is standpipe locn; arrows indicate drain path
existing dwv, in a nutshell
bath into vent-waste line
approx 13 in between clamp and dual fitting

I guess the only things to do are to quote the subject line in another area of the forums, "Why is everybody a plumber?", and wonder if plumbing is the only thing people become experts in after reading a book, and asking a friend some questions.
If I had a friend whose father was a brain surgeon, I would NOT let him work on my head. Knowledge is not passed by heredity or osmosis, so unless the friend was ALSO A PLUMBER, why would you ask him ANYTHING about plumbing?
1. where do you intend to connect it to?
2. If you are going to connect it to the 4" vertical line, it is too far away unless you add its own vent.

HJ: The friend is "plumbing knowledgeable" in that he's worked for his dad on a part-time basis for several years and has attended some of the requisite education to become a Journeyman Plumber. My description of him -and the reference to his father- was not meant to insult you (or any licensed professional.)

That said, to answer your questions:
1. I think there is only one option: into the approx. 13" section of the vertical line as shown in the last photo: if you concur, would a 3"x3"x2" sanitary-tee be the correct fitting?
2. I indicated in my post that I knew I'd need a separate vent, but sought advice as to its connection points and size: "Finally, I know that I also need a separate vent... it will start after the trap, and will connect above the existing, highest branch (?) vent that comes up from the two condos below. Does this need to be 2" or, will 1.5" be okay?" I think I would use a tee-wye to connect after the trap, and a sanitary tee to connect to the vertical (same as the existing line coming up from the condos below; see third photo.) I know that I also have to have a clean-out in the layout, too; where should this be?

I'd also very much like advice regarding the proximity of the two, long sweep 90s that will be needed to route the line through the walls (as depicted in the second photo.) The trap will be located at the spot marked with an X; it will then make the two 90s before heading towards the 3" vertical line. The finished floorspace of where the W/D will sit (shown as the foreground of X) is 27"w x 29"d, hence the approximation of 4' of the line in which the two 90s are needed. Will this configuration work, or will the restriction of the two 90s cause a problem with the discharge flow?

I hope you bought the stack unit already or studied the specs, because all that I have seen are "plumbed " on the right or left wall - or CAN BE. If the visuals dont disturb you, I would put the washer box on the face wall to the right of the pocket, right where you can see it. Now you lost most of your 90's.

If you are trying to go into that area above the clamp, I would buy a clamp on - glue on saddle t or y, which are hard to find but sold by most irrigation stores. Makes that job truly easy without moving any pipe. You simply drill into the ppe with a hole saw and file out the hole for good flow.

Probably only ok for a washer, which is force fed and not full of any large items.

Be careful of the dryer venting, they need to be placed quite carefully.

The washer box BEHIND a stack unit is a wish for trouble : no visual ability to inspect until water drips on your head downstairs.